Variable displacement vane pump

ABSTRACT

An object of the present invention is to provide a variable displacement vane pump capable of further reducing a pulse pressure. A vane pump ( 1 ) includes a cam ring ( 33 ). The cam ring ( 33 ) is annularly formed, and defines a plurality of pump chambers ( 38 ) on an inner peripheral side thereof in cooperation with a rotor ( 31 ) and vanes ( 32 ). An inner peripheral surface ( 330 ) of the cam ring ( 33 ) is formed in such a manner that, assuming that a confinement region refers to a region between an end portion of an intake port ( 221 ) and an end portion of a discharge port ( 222 ), at a timing when the pump chamber ( 38 ) communicates with or is disconnected from the discharge port ( 222 ) on one side corresponding to one of confinement regions or a timing close thereto, a change in a volume change amount of the pump chamber ( 38 ) on another side corresponding to the other of the confinement regions has an extreme value in a direction for reducing a change in a discharge amount at the time of the above-described communication/disconnection.

TECHNICAL FIELD

The present invention relates to a variable displacement vane pump.

BACKGROUND ART

Conventionally, there has been known a variable displacement vane pumpincluding a cam ring. For example, in a pump discussed in PTL 1, aninner peripheral surface of a cam ring has an adjusted shape with anattempt to reduce pulsation of a pressure (a pulse pressure).

CITATION LIST Patent Literature

PTL 1: Japanese Patent Application Public Disclosure No. 2013-32739

SUMMARY OF THE INVENTION Technical Problem

However, the conventional vane pump has left room to further reduce thepulse pressure.

Solution to Problem

In a vane pump according to one aspect of the present invention, aninner peripheral surface of a cam ring is formed in such a manner that,at a timing when a pump chamber communicates with or is disconnectedfrom a discharge port on one side corresponding to one of confinementregions or a timing close thereto, a change in a volume change amount ofa pump chamber on another side corresponding to the other of theconfinement regions has an extreme value in a direction for reducing achange in a discharge amount at the time of the above-describedcommunication/disconnection.

Therefore, the pulse pressure can be further reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial cross-sectional view of a vane pump according to afirst embodiment.

FIG. 2 is a cross-sectional view along a direction perpendicular ororthogonal to an axis of the vane pump according to the firstembodiment.

FIG. 3 illustrates a characteristic of a relationship between a changerate of a vane projection amount with respect to a rotor rotationalamount and the rotor rotational amount in a confinement region in amaximum eccentricity state of a cam ring in the vane pump according tothe first embodiment.

FIG. 4 illustrates a characteristic of a relationship between the changerate of the vane projection amount with respect to the rotor rotationalamount and the rotor rotational amount in the confinement region in a ⅓eccentricity state of the cam ring in the vane pump according to thefirst embodiment.

FIG. 5 illustrates a characteristic of a relationship between the changerate of the vane projection amount with respect to the rotor rotationalamount and the rotor rotational amount in a second confinement region inthe maximum eccentricity state and the ⅓ eccentricity state of the camring in the vane pump according to the first embodiment.

FIG. 6 illustrates a characteristic of a relationship between the changerate of the vane projection amount with respect to the rotor rotationalamount and the rotor rotational amount in the second confinement regionin the minimum eccentricity state and the ⅓ eccentricity state of thecam ring in each of the vane pump according to the first embodiment anda vane pump according to a comparative example.

FIG. 7(a) illustrates a characteristic of a relationship between a sumof change rates of volumes of all pump chambers in communication with adischarge port with respect to the rotor rotational amount, and therotor rotational amount in the ⅓ eccentricity state of the cam ring inthe vane pump according to the first embodiment. FIG. 7(b) illustrates acharacteristic of a relationship between the change rate of the volumeof each of the pump chambers in communication with the discharge portwith respect to the rotor rotational amount, and the rotor rotationalamount in the ⅓ eccentricity state of the cam ring in the vane pumpaccording to the first embodiment.

FIG. 8 illustrates a characteristic of a relationship between the changerate of the vane projection amount with respect to the rotor rotationalamount and the rotor rotational amount in the confinement region in themaximum eccentricity state of the cam ring in a vane pump according to asecond embodiment.

FIG. 9 illustrates a characteristic of a relationship between the changerate of the vane projection amount with respect to the rotor rotationalamount and the rotor rotational amount in the confinement region in the⅓ eccentricity state of the cam ring in the vane pump according to thesecond embodiment.

DESCRIPTION OF EMBODIMENTS First Embodiment [Configuration]

First, a configuration will be described. FIG. 1 is a cross-sectionalview illustrating a vane pump (hereinafter referred to as a pump) 1according to a first embodiment, taken along a plane passing through ashaft center (a rotational axis of a rotor 31) O, which is a center of arotation of a driving shaft 30. FIG. 2 corresponds to a cross-section asviewed from a line II-II in FIG. 1. FIG. 1 corresponds to across-section as viewed from a line I-I in FIG. 2. For convenience ofthe description, a tree-dimensional orthogonal coordinate system is setup. An x axis and a y axis extend in a radial direction of the drivingshaft 30 (with respect to the shaft center O), and a z axis extendsalong the shaft center O. The z axis is a direction along the rotationalaxis of the driving shaft 30. The x axis extends in a direction in whicha cam ring 33 swings, and the y axis is perpendicular or orthogonal tothe x axis and z axis. An x-axis positive direction is defined to be oneside closer to the shaft center O with respect to a central axis P ofthe cam ring 33. A y-axis positive direction is defined to be one sidecloser to a control portion 4 with respect to a pump portion 3. A z-axispositive direction is defined to be one side closer to a front body 21with respect to a rear body 20. The pump 1 is used as a hydraulic supplysource of a device mounted on a vehicle. More specifically, the pump 1is used for a power steering apparatus for reducing a required force ofoperating a steering wheel of the vehicle. The pump 1 is driven by acrank shaft of an internal combustion engine (an engine), and introducesand discharges hydraulic liquid as hydraulic fluid. The hydraulic liquidis, for example, oil. The pump 1 is a variable displacement pump capableof changing a discharge capacity (an amount of liquid discharged perrotation, a pump capacity). The pump 1 is a pump unit including a pumphousing 2, the pump portion 3, and the control portion 4. The pumpportion 3 introduces and discharges the hydraulic liquid. The controlportion 4 controls the pump capacity.

The pump housing 2 includes the rear body 20, the front body 21, and aside plate 22. The rear body 20 includes therein a recessed portion 200,a low-pressure chamber, a high-pressure chamber 201, a connection port202, a valve containing hole 203, a spring containing hole 204, abearing mounting portion 205, a hole 206, a liquid passage 207, and thelike. The recessed portion 200 has a bottomed cylindrical shape, andextends in the z-axis direction to be opened at a surface of the rearbody 20 on a z-axis positive direction side. The low-pressure chamberand the high-pressure chamber 201 are recessed portions provided at abottom portion 200 a of the recessed portion 200, and are opened at thebottom portion 200 a. The connection port 202 extends in the x-axisdirection inside an x-axis positive direction side, a y-axis positivedirection side, and the z-axis positive direction side of the rear body20, and is opened at an outer surface of the rear body 20 on the x-axispositive direction side. A member (a liquid passage forming member) 23in which a liquid passage 230 is formed is set in the connection port202. The connection port 202 (the member 23) is connected to, forexample, a power cylinder of the power steering apparatus via a pipe.The valve containing hole 203 extends in the x-axis direction inside they-axis positive direction side and the z-axis positive direction side ofthe rear body 20, and is opened at an outer surface of the rear body 20on an x-axis negative direction side. A plug member 24 is fixed in anopening of the valve containing hole 203. The spring containing hole 204extends in the x-axis direction inside an x-axis positive direction sideand a z-axis positive direction side of a wall portion 200 b surroundingthe recessed portion 200, and is opened at an inner peripheral surfaceof the recessed portion 200 and the outer surface of the rear body 20 onx-axis positive direction side. A plug member 25 is fixed to an openingof the spring containing hole 204 on the outer surface of the rear body20. The bearing mounting portion 205 has a bottomed cylindrical shape,and extends in the z-axis direction to be opened at a surface of therear body 20 on a z-axis negative direction side. A bearing 27 ismounted on the bearing mounting portion 205. The bearing 27 is, forexample, a ball bearing. The hole 206 extends in the z-axis direction toextend through the rear body 20, and is opened to the bottom portion 200a of the recessed portion 200 and a bottom portion 205 a of the bearingmounting portion 205. An intake liquid passage inside the rear body 20connects the low-pressure chamber to a reservoir tank. The dischargeliquid passage 207 connects the high-pressure chamber 201 to theconnection port 202. A metering orifice 207 a is provided in thedischarge liquid passage 207. A first control liquid passage 401connects the connection port 202 to an end of the valve containing hole203 in the x-axis positive direction. A second control liquid passage402 connects the high-pressure chamber 201 to an end of the valvecontaining hole 203 in the x-axis negative direction. A damper orifice402 a is provided in the second control liquid passage 402. A thirdcontrol liquid passage 403 connects an x-axis negative direction side ofthe valve containing hole 203 to the recessed portion 200.

The front body 21 includes a bearing mounting portion 211. The bearingmounting portion 211 has a bottomed cylindrical shape, and extends inthe z-axis direction to be opened at a surface 210 of the front body 21on the z-axis negative direction side. A bearing 28 is mounted on thebearing mounting unit 211. The bearing 28 is, for example, a needlebearing. The front body 21 is mounted on the z-axis positive directionside of the rear body 20, and is fixed to the rear body 20 by bolts 29.The front body 21 closes the opening of the recessed portion 200.

The side plate 22 is a disk-like member (a pressure plate), and iscontained in the recessed portion 200 and mounted at the bottom portion200 a. A circumferential position of the side plate 226 in the recessedportion 200 is determined by being fixed to the rear body 20 (the bottomportion 200 a of the recessed portion 200) due to a pin 35 extendingthrough a hole of the side plate 22. A hole 226 extends through in thez-axis direction a generally central position of the side plate 22. Asurface 220 of the side plate 22 on the z-axis positive direction sideis a flat surface, and includes an intake opening (an intake port) 221,a discharge opening (a discharge port) 222, an intake-side backpressureport 223, and a discharge-side backpressure port 224 as bottomedrecessed portions (grooves). The intake port 221 is located on they-axis positive direction side with respect to the shaft center O, andextends along a circular arc centered at the shaft center O. An endportion 221 a on the x-axis positive direction side is a start endportion of the intake port 221, and an end portion 221 b on the x-axisnegative direction side is a terminating end portion of the intake port221. A hole is opened at a bottom portion of the intake port 221. Thehole extends through the side plate 22 in the z-axis direction. Theintake port 221 is connected to the low-pressure chamber of the rearbody 20 via the above-described hole. The discharge port 222 is locatedon the y-axis negative direction side with respect to the shaft centerO, and extends along a circular arc centered at the central axis 0. Anend portion 222 a on the x-axis negative direction side is a start endportion of the discharge port 222, and an end portion 222 b on thex-axis positive direction side is a terminating end portion of thedischarge port 222. A hole is opened at a bottom portion of thedischarge port 222. The hole extends through the side plate 22 in thez-axis direction. The discharge port 222 is connected to thehigh-pressure chamber 201 via the above-described hole. The dischargeport 222 includes a notch portion 225 on a start end portion 222 a sidethereof. The start end portion 222 a of the discharge point 222 is alsoa start end portion of the notch portion 225. The notch portion 225 hasa flattened (flat) rectangular shape in cross-section taken along theradial direction of the rotor 31. The notch portion 255 is smaller thana main body portion of the discharge port 222 in area in cross-sectiontaken along the radiation direction of the rotor 31. No notch portion isprovided on a terminating end portion 222 b side of the discharge port222. The end portion 221 b of the intake port 221 faces the start endportion 222 a of the discharge port 222, and the start end portion 221 aof the intake port 221 faces the terminating end portion 222 b of thedischarge port 222 in a direction of the rotation of the rotor 31 (thedriving shaft 30) that is centered at the shaft center O (hereinafterreferred to a circumferential direction).

The intake-side backpressure port 223 is basically located on the y-axispositive direction side with respect to the shaft center O, and extendsalong a circular arc centered at the shaft center O on one side closerto the shaft center O (a radially inner side) with respect to the intakeport 221. A hole is opened at a bottom portion of the port 223. The holeextends through the side plate 22 in the z-axis direction. The port 223is connected to the high-pressure chamber 201 via the above-describedhole. The discharge-side backpressure port 224 is basically located onthe y-axis negative direction side with respect to the shaft center O,and extends along a circular arc centered at the shaft center O on aradially inner side with respect to the discharge port 222. A hole isopened at a bottom portion of the port 224. The hole extends through theside plate 22 in the z-axis direction. The port 224 is connected to thehigh-pressure chamber 201 via the above-described hole. An end portionof the intake-side backpressure port 223 faces a start end portion ofthe discharge-side backpressure port 224, and a start end portion of theport 223 faces an end portion of the port 224 in the circumferentialdirection. Similar ports and the like are also formed on the surface 210of the front body 21 on the z-axis negative direction side incorrespondence with the ports 222 and 221 and the ports 223 and 224 ofthe side plate 22.

The pump portion 3 includes the driving shaft 30, the rotor 31, aplurality of vanes 32, the cam ring 33, and an adaptor ring 34. Thedriving shaft 30 is supported on the pump housing 2, and is rotationallydriven by the crank shaft. The driving shaft 30 is mounted in the hole206 of the rear body 20, and extends through inside the hole 226 of theside plate 22. An end of the driving shaft 30 on the z-axis positivedirection side is rotatably supported on the front body 21 by thebearing 28. A z-axis negative direction side of the driving shaft 30 isrotatably supported on the rear body 20 by the bearing 27. The rotor 31,the plurality of vanes 32, the cam ring 33, and the adaptor ring 34 arecontained in the recessed portion 200 on the z-axis positive directionside of the side plate 22. These components such as the rotor 31function as pump elements, and the recessed portion 200 functions as apump element containing portion.

The rotor 31 has a generally cylindrical shape, and extends in thez-axis direction while being coupled to the driving shaft 30 byserration coupling, thereby being rotationally driven by the drivingshaft 30. The rotor 31 rotates in a counterclockwise direction in FIG. 2about the shaft center O. The rotor 31 includes a plurality of slots 311in the circumferential direction. The slots 311 are bottomed grooves(slits), and extend in the radial direction of the rotor 31 inside therotor 31 to be opened at an outer peripheral surface 310 of the rotor31. The slots 311 extend throughout an entire range of the rotor 31 inthe z-axis direction. The number of slots 311 is an odd number (eleven).The plurality of slots 311 is disposed at generally even intervals inthe circumferential direction. A proximal end 312 of each of the slots311 on a radially inner side of the rotor 31 (one side toward the shaftcenter O) has a cylindrical shape extending in the z-axis direction thatis larger in diameter than a circumferential width of a main body of theslot 311. The proximal end 312 is connected to the backpressure ports223 and 224. Each of the vanes 32 is a plat-like member contained ineach of the slots 311 one by one, and is movable by projecting andretracting (movable in a manner projectable and retractable) from andinto the rotor 31. The number of vanes 32 is an odd number (eleven).Between the proximal end 312 of the slot 311 and the vane 32 containedin this slot 311, a backpressure chamber (a pressure-receiving portion)36 of this vane 32 is formed.

The cam ring 33 is annularly formed and disposed so as to surround therotor 31, and is provided movably in the recessed portion 200. The camring 33, the rotor 31 (the slots 311), and the vanes 32 have dimensionsin the z-axis direction that are generally equal to one another. Aninner peripheral surface 330 of the cam ring 33 has a generallycylindrical shape extending in the z-axis direction. An outercircumferential surface 331 of the cam ring 33 has a cylindrical shapegenerally coaxially with the inner peripheral surface 330. A centralaxis of the inner peripheral surface 330 (the outer peripheral surface331) will be hereinafter referred to as a central axis P of the cam ring33. A recessed portion 332 is provided on an outer periphery of the camring 33 on the y-axis negative direction side. The recessed portion 332has a half cylinder shape extending in the z-axis direction. The adaptorring 34 is annularly formed and is fitted to the recessed portion 200.The adaptor ring 34 is disposed so as to surround the cam ring 33. Theadaptor ring 34 includes a large-diameter hole 344 and a small-diameterhole 345 extending through an inner periphery and an outer peripherythereof, respectively. The hole 344 is located on the x-axis positivedirection side and surrounds the opening of the spring containing hole204 in the recessed portion 200 of the rear body 20. The hole 345 islocated on the y-axis positive direction side and is connected to thethird control liquid passage 403 opened at the recessed portion 200 ofthe rear body 20. A first support surface 341, a second support surface342, and a third support surface 343 are formed on an inner peripheralsurface 340 of the adaptor ring 34. The first support surface 341 ispositioned on the y-axis positive direction side and is a flat surfaceextending in the z-axis direction. A seal groove 346 extending in thez-axis direction is formed on the first support surface 341 at aposition slightly offset from the shaft center O toward the x-axisnegative direction side. A seal member 37 is provided in the seal groove346. The second support surface 342 is a recessed curved surfaceprotruding in a direction away from the shaft center O that ispositioned slightly offset from the shaft center O toward the x-axisnegative direction side and located on the y-axis negative directionside while extending in the z-axis direction. A half-cylindricalrecessed portion 347 extending in the z-axis direction is provided onthe second support surface 342 at a position slightly offset from theshaft center O toward the x-axis negative direction side. The thirdsupport surface 343 is a flat surface located on the x-axis negativedirection side and extending in the z-axis direction.

The cam ring 33 is swingably provided on the inner peripheral side ofthe adaptor ring 34. The pin 35 is provided between the recessed portion347 of the adaptor ring 34 and the recessed portion 332 of the cam ring33. The pin 35 extends in the z-axis direction, and is fixed to the pumphousing 2 (the rear body 20 and the front body 21). The cam ring 33 isswingable about the pin 35 or a vicinity thereof. A y-axis positivedirection side of the outer peripheral surface 331 of the cam ring 33 isin contact with the seal member 37. A y-axis negative direction side ofthe outer peripheral surface 331 is in contact with the second supportsurface 342. The cam ring 33 is swingable in an xy plane with a supportpoint therefor set to a line tangential to the second support surface342. During a swinging movement, the cam ring 33 moves so as to slightlyroll on the second support surface 342. At this time, the pin 35prevents or reduces a positional shift of the cam ring 33 in thedirection of the rotation (a relative rotation) relative to the adaptorring 34. A swinging movement of the cam ring 33 toward the x-axispositive direction side is regulated by, for example, abutment of theouter peripheral surface 331 with the inner peripheral surface 340 ofthe adaptor ring 34. A swinging movement of the cam ring 33 toward thex-axis negative direction side is regulated by abutment of the outerperipheral surface 331 with the third support surface 343. Aneccentricity amount δ will be defined to be a displacement amount of thecentral axis P from the shaft center O. The eccentricity amount δ isminimized at a position where the outer peripheral surface 331 is inabutment with the inner peripheral surface 340 on the x-axis positivedirection side (a minimum eccentricity position). The eccentricityamount δ is maximized at a position illustrated in FIG. 2 where theouter peripheral surface 331 is in abutment with the third supportsurface 343 (a maximum eccentricity position). A coil spring 44 as anelastic member is provided on the outer peripheral side of the cam ring33 on the x-axis positive direction side. The spring 44 is provided inthe spring containing hole 204 of the rear body 20, and one end sidethereof is supported by the plug member 25. An opposite end side of thespring 44 is in contact with the outer peripheral surface 331 of the camring 33. The spring 44 is provided in a compressed state, and constantlybiases the cam ring 33 relative to the rear body 20 toward the x-axisnegative direction side (in a direction for increasing δ).

First and second chambers 41 and 42 are formed on the outer peripheralside of the cam ring 33 by the cam ring 33 and the adaptor ring 34. Aspace between the inner peripheral surface 340 and the outer peripheralsurface 331 has an opening on the z-axis negative direction side that issealingly closed by the side plate 22, and an opening on the z-axispositive direction side that is sealingly closed by the front body 21.The above-described space is liquid-tightly divided into the twochambers 41 and 42 by a contact portion between the second supportsurface 342 and the outer peripheral surface 331, and a contact portionbetween the seal member 37 and the outer peripheral surface 331. Thefirst chamber 41 is formed on the x-axis positive direction side, andthe second chamber 42 is formed on the x-axis negative direction side.The hole 345 is opened to the second chamber 42. The second chamber 42is connected to the third control liquid passage 403 via this hole 345.The second chamber 42 functions as a fluid pressure chamber (a controlpressure chamber). The first chamber 41 is opened to an atmosphericpressure via, for example, a drain liquid passage.

A distance between the surface 220 of the side plate 22 on the z-axispositive direction side and the surface 210 of the front body 21 on thez-axis negative direction side is slightly larger than the dimensions ofthe rotor 31, the vanes 32, and the cam ring 33 in the z-axis direction.An annular space is formed among the outer peripheral surface 310 of therotor 31, the inner peripheral surface 330 of the cam ring 33, thesurface 220 of the side plate 22, and the surface 210 of the front body21. This annular space is divided into a plurality of pump chambers(vane chambers) 38 by the plurality of vanes 32. In other words, the camring 33 forms the plurality of pump chambers 38 on the inner peripheralside thereof in cooperation with the rotor 31 and the vanes 32. Thenumber of pump chambers 38 is an odd number (eleven). Hereinafter, acircumferential distance between the circumferentially adjacent vanes 32(an angle around the shaft center O) will be referred to as one pitch(1P). Then, the circumferential distance between the vanes 32 is, forexample, a circumferential distance (an angle) between a circumferentialcenter of some vane 32 and a circumferential center of the vane 32circumferentially adjacent to the above-described vane 32.Alternatively, this distance is a circumferential distance (an angle)between a surface of some vane 32 on one circumferential side (forexample, one side located in a direction of a reverse rotation of therotor 31) and a surface of the vane 32 circumferentially adjacent to theabove-described vane 32 on the above-described one circumferential side.A circumferential dimension of one pump chamber 38 is little shorterthan one pitch (a size acquired by subtracting the circumferentialdimension of the vane 32 from one pitch). The start end portion 221 a ofthe intake port 221 is located approximately half pitch (½P) away from astraight line passing through the shaft center O and extending inparallel with the x axis, toward the y-axis positive direction side (oneside located in the direction of the rotation of the rotor 31). The endportion 221 b of the intake port 221 is located approximately half pitchaway from the above-described straight line toward the y-axis positivedirection side (an opposite side located in the direction of the reverserotation of the rotor 31). The start end portion 222 a of the dischargeport 222 (the notch portion 25) is located approximately half pitch awayfrom the above-described straight line toward the y-axis negativedirection side (the one side located in the direction of the rotation ofthe rotor 31). The end portion 222 b of the discharge port 222 islocated approximately half pitch away from the above-described straightline toward the y-axis negative direction side (the opposite sidelocated in the direction of the reverse rotation of the rotor 31). Acircumferential distance between the portions 222 b and 221 a and acircumferential distance between the portions 221 b and 222 a are eachapproximately one pitch.

A distance between the outer peripheral surface 310 of the rotor 31 andthe inner peripheral surface 330 of the Cam ring 33 in the radialdirection of the rotor 31 increases from the x-axis positive directionside toward the x-axis negative direction side, with the cam ring 33(the central axis P) positioned eccentrically from the rotor 31 (theshaft center O) toward the x-axis negative direction side. The vanes 32project and retract from and into the slots 311 according to this changein the distance, thereby liquid-tightly defining the respective pumpchambers 38. The pump chamber 38 on the x-axis negative direction sidehas a larger volume v than the pump chamber 38 on the x-axis positivedirection side. Due to this difference in the volume v of the pumpchamber 38, the volume v of the pump chamber 38 is increasing on they-axis positive direction side with respect to the shaft center O as thepump chamber 38 is traveling toward the x-axis negative direction side,which is the direction of the rotation of the rotor 31 (thecounterclockwise direction in FIG. 2). On the other hand, the volume vof the pump chamber 38 is reducing on the y-axis negative direction sidewith respect to the shaft center O as the pump chamber 38 is travelingtoward the x-axis positive direction side, which is the direction of therotation of the rotor 31. A region in which the volume v of each of theplurality of pump chambers 38 increases according to the rotation of therotor 31 (a section on the y-axis positive direction side) is an intakeregion. A region in which the volume v of each of the plurality of pumps38 reduces according to the rotation of the rotor 31 (a section on they-axis negative direction side) is a discharge region. The intake port221 is opened to the intake region, and the discharge port 222 is openedto the discharge region. The pump chamber 38 located in the intakeregion is in communication with the intake port 221 and the pump chamber38 located in the discharge region is in communication with thedischarge port 222 regardless of the eccentricity amount δ. A regionbetween the terminating end portion 221 b of the intake port 221 and thestart end portion 222 a of the discharge port 222 (the notch portion225) is a first confinement region A. A region between the terminatingend portion 222 b of the discharge port 222 and the start end portion221 a of the intake port 221 is a second confinement region B. Both theregions A and B are each approximately one pitch (1P). The pair ofsurfaces 210 and 220 facing each of the regions A and B in the z-axisdirection in the pump housing 2 are each formed into a flat surface. Inother words, no recessed portion (groove) and no hole are provided onthe surfaces 210 and 220 in each of the regions A and B. These surfaces210 and 220 are disposed generally in parallel with each other. Each ofthe regions A and B confines the hydraulic liquid in the pump chambers38 located in their own regions, thereby preventing the discharge port222 (including the notch 225) and the intake port 221 from communicatingwith each other via the pump chambers 38.

When the rotor 31 rotates with the cam ring 33 (the central axis P)positioned eccentrically from the rotor 31 (the shaft center O) towardthe x-axis negative direction side, the pump chambers 38 periodicallyrepeat an increase and a reduction of the volume v while rotating aroundthe shaft center O. The pump chamber 38 in communication with the intakeport 221 in the intake region introduces therein the hydraulic liquidfrom the intake port 221. The pump chamber 38 in communication with thedischarge port 222 in the discharge region discharges the hydraulicliquid to the discharge port 222. The pump chambers 38 areliquid-tightly maintained out of communication with both the intake port221 and the discharge port 222 (the notch portion 225) in each of theregions A and B. A discharge pressure is applied to the backpressurechamber 36 of the vane 32 via the backpressure port 223 or 224.Therefore, a performance of the vane 32 regarding the projection, forexample, when the number of rotations of the pump is small, can beimproved, whereby the liquid-tightness of the pump chambers 38 can beimproved.

The control portion 4 is provided in the rear body 20, and includes theliquid passages 207 and 401 to 403, the chambers 41 and 42, a controlvalve 43, the coil spring 44, and a relief valve 45. The control valve43 is a spool valve, and includes a spool 43 a and a coil spring 43 b.The spool 43 a and the spring 43 b are provided in the valve containinghole 203. The spool 43 a is a valve body that switches a flow passage,and includes a first land 431 and a second land 432. The first land 431defines a pressure chamber 433 and a drain chamber 434 in the valvecontaining hole 203. The second control liquid passage 402 is normallyor constantly opened to the pressure chamber 433. The drain liquidpassage is normally or constantly opened to the drain chamber 434. Thedrain liquid passage is opened to the atmospheric pressure. The secondland 432 defines the drain chamber 434 and a spring chamber 435 in thevalve containing hole 203. The first control liquid passage 401 isnormally or constantly opened to the spring chamber 435. The coil spring43 b is an elastic member, and is set in the spring chamber 435. One endside of the spring 43 b is in contact with the bottom portion of thevalve containing hole 203 on the x-axis positive direction side, and anopposite end side of the spring 43 b is in contact with an end of thespool 43 a on the x-axis positive direction side. The spring 43 b is setin a compressed state, and constantly biases the spool 43 a relative tothe rear body 20 toward the x-axis negative direction side. The firstland 431 is located slightly offset toward the x-axis negative directionside from the opening of the third control liquid passage 403 on theinner peripheral surface of the valve containing hole 203 with the spool43 a maximally displaced toward the x-axis negative direction side asillustrated in FIG. 2. The first land 431 blocks the communicationbetween the pressure chamber 433 and the liquid passage 403 and alsoestablishes communication between the drain chamber 434 and the liquidpassage 403. The relief valve 45 is a normally-closed valve set at thespool 43 a, and is opened when a pressure in the spring chamber 435reaches or exceeds a predetermined pressure to establish communicationbetween the spring chamber 435 and the drain chamber 434.

A pressure in the pressure chamber 433 and a pressure in the springchamber 435 are applied to both axial ends of the spool 43 a fromopposite directions from each other. The pressure in the pressurechamber 433 is a discharge pressure on an upstream side of the meteringorifice 207 a that is supplied from the high-pressure chamber 201 (thedischarge port 222) of the rear body 20 via the second control liquidpassage 402. The pressure in the spring chamber 435 is a dischargepressure on a downstream side of the orifice 207 a that is supplied fromthe high-pressure chamber 201 (the discharge port 222) of the rear body20 via the discharge liquid passage 207 and the first control liquidpassage 401. A pressure loss at the orifice 207 a increases according toan increase in the number of rotations of the pump 1 (a discharge flowamount), so that the discharge pressure on the downstream side of theorifice 207 a falls below the discharge pressure on the upstream side ofthe orifice 207 a. A difference between these upstream and downstreamdischarge pressures (hereinafter referred to as a differential pressure)generates a force biasing the spool 43 a in the x-axis positivedirection. When the biasing force due to this differential pressureexceeds the above-described biasing force of the spring 43 b, the spool43 a is displaced in the x-axis positive direction. The first land 431blocks communication between the drain chamber 434 and the third controlliquid passage 403, and also establishes the communication between thepressure chamber 433 and the liquid passage 403. As a result, the secondchamber 42 and the pressure chamber 433 are brought into communicationwith each other, allowing the hydraulic liquid to be supplied from thechamber 433 to the second chamber 42. When the force with which the camring 33 is biased by the pressure in the second chamber 42 in the x-axispositive direction exceeds a sum of the pressure in the first chamber 41(the atmospheric pressure) and the force with which the cam ring 33 isbiased by the coil spring 44 in the x-axis negative direction, the camring 33 swings in the x-axis positive direction, followed by a reductionin the eccentricity amount δ. As a result, the pomp capacity reduces. Onthe other hand, when the biasing force due to the differential pressurefalls below the above-described biasing force of the spring 43 b, thespool 43 a is displaced in the x-axis negative direction. The first land431 blocks the communication between the pressure chamber 433 and theliquid passage 403, and also establishes the communication between thedrain chamber 434 and the liquid passage 403. As a result, the pressurein the second chamber 42 reduces, so that the cam ring 33 swings in thex-axis negative direction, followed by an increase in the eccentricityamount δ. Due to that, the pump capacity increases. In this manner, thecontrol valve 43 controls the inflow of the hydraulic liquid into thesecond chamber 42 and the outflow of the hydraulic liquid from thechamber 42 according to the number of rotations of the pump 1 (thedischarge flow amount), thereby varying the pump capacity. The controlportion 4 such as the control valve 43 functions as a cam ring controlmechanism that controls the eccentricity amount δ. A fixed capacityregion is such a region where the number of rotations of the pump issmall that the eccentricity amount δ is kept maximized and the pumpcapacity is kept constant even when the number of rotations of the pumpchanges. A variable capacity region is such a region where the number ofrotations of the pump is large that the eccentricity amount δ reducesand the pump capacity reduces according to an increase in the number ofrotations of the pump.

The inner peripheral surface 330 of the cam ring 33 is formed in thefollowing manner. Hereinafter, focusing on two vanes 32 forming somesingle pump chamber 38, the vane 32 on the one side located in thedirection of the rotation of the rotor 31 will be referred to as a frontvane 32, while the vane 32 on the opposite side located in the directionof the reverse rotation of the rotor 31 will be referred to as a rearvane 32. A distance from the shaft center O to the inner peripheralsurface 330 of the cam ring 33 (a movement radius) will be referred toas a vane projection amount r. A rotational angle of the rotor 31 willbe referred to as a rotational amount θ of the rotor 31. A distance fromthe outer peripheral surface 310 (the opening of the slot 311) of therotor 31 to the inner peripheral surface 330 of the cam ring 33 may beused as the vane projection amount r. Further, a rotational speed of therotor 31 may be used as the rotor rotational amount θ. FIGS. 3 to 6 arecharacteristic diagrams each illustrating a relationship between achange rate dr/dθ of the amount r with respect to θ, and θ. Assume thata sign of θ is positive in the direction of the rotation of the rotor 31(negative in the direction of the reverse rotation of the rotor 31).When the sign of dr/dθ is positive, the amount r increases according tothe rotation of the rotor 31. When the sign of dr/dθ is negative, theamount r reduces according to the rotation of the rotor 31. FIG. 3illustrates the above-described relationship in the first confinementregion A, the second confinement region B, and vicinities of theseregions A and B in such a state that the cam ring 33 is located at aposition where the eccentricity amount δ is maximized (hereinafterreferred to a maximum eccentricity state). FIG. 4 illustrates theabove-described relationship in the regions A and B and the vicinitiesof these regions A and B in such a state that the cam ring 33 is movedby ⅓ of the entire eccentricity amount δ from the position where theamount δ is maximized toward a position where the amount δ is minimized(in the x-axis positive direction) (hereinafter referred to as a ⅓eccentricity state). FIG. 5 illustrates the above-described relationshipin the region B and the vicinity thereof in each of the maximumeccentricity state and the ⅓ eccentricity state. FIG. 6 illustrates theabove-described relationship in the region B and the vicinity thereof insuch a state that the cam ring 33 is located at the position where theamount δ is minimized (hereinafter referred to as a minimum eccentricitystate), and the ⅓ eccentricity state. A characteristic of a comparativeexample is indicated by a long dashed double-dotted line.

(Maximum Eccentricity State)

As illustrated in FIG. 3, the sign of the change rate dr/dθ is negativein the entire range of the first confinement region A in the maximumeccentricity state. In other words, the vane projection amount rconstantly reduces as the vane 32 travels from the terminating endportion 221 b of the intake port 221 (corresponding to a rotationalamount θ_(1S)) toward the start end portion 222 a of the discharge port222 (corresponding to a rotational amount θ_(1E)) according to therotation of the rotor 31. As illustrated in FIG. 5, the sign of dr/dθ isnegative in the entire range of the second confinement region B in themaximum eccentricity state. In other words, the amount r constantlyreduces as the vane 32 travels from the terminating end portion 222 b ofthe discharge port 222 (corresponding to a rotational amount θ_(2S)) tothe start end portion 221 a of the intake port 221 (corresponding towarda rotational amount θ_(2E)) according to the rotation of the rotor 31.

(⅓ Eccentricity State)

As illustrated in FIG. 4, the sign of dr/dθ is negative in the entirerange of the first confinement region A in the ⅓ eccentricity state. Inother words, the amount r constantly reduces as the vane 32 travels fromthe terminating end portion 221 b (θ_(1S)) of the intake port 221 towardthe start end portion 222 a (θ_(1E)) of the discharge port 222. Further,the amount r gradually reduces as the vane 32 travels from θ_(1S) towardθ_(1E). An absolute value of dr/dθ (the negative value) graduallyreduces, and then gradually increases after reaching an extremely smallvalue dr/dθ₁* at θ₁*, as the vane 32 travels from θ_(1S) toward θ_(1E).θ₁* is located in a range from ⅓ pitch to ⅔ pitch from θ_(1S) inclusive.In other words, the point θ₁* is located between a point θ_(1(1/3))positioned ⅓ pitch (⅓p) away from θ_(1S) and a point θ_(1(2/3))positioned ⅔ pitch (⅔P) away from θ_(1S). The region A is one pitch(1P). Therefore, θ₁* is located in a range of a central portion when theregion A is divided into three portions (θ_(1(1/3)) to θ_(1(2/3))). Morespecifically, θ₁* is located slightly offset toward the θ_(1S) side froma point θ_(1(1/2)) positioned ½ pitch (½P) away from θ_(1S). Assume thatΔ1 (a first change gradient) represents a gradient of a change in dr/dθsince the absolute value of dr/dθ starts reducing until reaching theextremely small value dr/dθ₁* (more specifically, a change from θ_(1S)to θ₁*) in the region A in the ⅓ eccentricity state. Δ1 isΔ1=|dr/dθ₁*−dr/dθ_((1S))|/|θ₁*−θ_(1S)|. Assume that Δ2 (a second changegradient) represents a gradient of a change in dr/dθ since the absolutevalue of dr/dθ reaches the extremely small value dr/dθ₁* until stoppingincreasing (more specifically, a change from θ₁* to θ_(1E)). Δ2 isΔ2=|dr/dθ₁*−dr/dθ_((1E))|/|θ₁*−θ_(1E)|. Δ2 is greater than Δ1 (Δ1<Δ2).In other words, the absolute value Δ2 of an average change rate of dr/dθon a second half side of the region A (when the absolute value of dr/dθis increasing) is greater than the absolute value Δ1 of an averagechange rate of dr/dθ on a first half side of the region A (when theabsolute value of dr/dθ is reducing). In the present embodiment, Δ2/Δ1,i.e., a ratio of Δ2 to Δ1 is approximately 1.24. As illustrated in FIGS.5 and 6, the sign of dr/dθ is switched from negative to positive atθ_(2M) in the direction of the rotation of the rotor 31 in the secondconfinement region B in the ⅓ eccentricity state. In other words, as thevane 32 travels from the terminating end portion 222 b (θ_(2S)) of thedischarge port 222 toward the start end portion 221 a (θ_(2E)) of theintake port 221, the amount r gradually reduces, and then graduallyincreases after reaching an extremely small value at θ_(2M). The amountr gradually increases in the region B at least in a partial (a θ_(2E)side) range (θ_(2M) to θ_(2E)) continuous from the terminating endportion (θ_(2E)) thereof.

(Minimum Eccentricity State)

As illustrated in FIG. 6, a function of dr/dθ with respect to θ has anextreme value dr/dθ₂* at θ₂* in the second confinement region B in theminimum eccentricity state. In other words, there are a θ region wherethe change rate of dr/dθ with respect to θ (a second-order differentialof the amount r with respect to θ, a slope of the above-describedfunction) has a negative value, and a θ region where this change ratehas a positive value. The change rate of dr/dθ has a negative value in aregion Ba on a first half side of the region B, and has a positive valuein a region Bb on a second half side of the region B. Whether dr/dθincreases or reduces changes at the point θ₂* separating the regions Baand Bb according to the rotation of the rotor 31 (the function of theamount r with respect to θ has an inflection point at θ₂*).

[Function]

Next, a function will be described. The volume v of each of the pumpchambers 38 changes (increases or reduces) according to the rotation ofthe rotor 31 with the cam ring 33 positioned eccentrically. An amountdv/dθ of the change in the volume v of some pump chamber 38 with respectto the rotational amount θ of the rotor 31 (in other words, an amount ofthe change in the volume per rotor rotational amount) correlates withthe change rate dr/dθ of the vane projection amount r with respect to θat each of the positions of the two vanes 32 sandwiching this pumpchamber 38. A function of dv/dθ with respect to θ can be drawn in agenerally same form as the function of dr/dθ with respect to θ. Thechange amount dv/dθ of the pump chamber 38 communicating with thedischarge port 222 while overlapping either the confinement region A orB can be approximated by, for example, dr/dθ at the position of the rearvane 32 (passing through the region A) of the two vanes 32 sandwichingthis pump chamber 38 on the region A side. The change amount dv/dθ canbe approximated by dr/dθ at the position of the front vane 32 (passingthrough the region B) of the two vanes 32 sandwiching this pump chamber38 on the region B side.

FIG. 7(b) is a characteristic diagram illustrating a relationshipbetween dv/dθ of each of the pump chambers 38 in communication(connection) with the discharge port 222, and θ in the ⅓ eccentricitystate. FIG. 7(b) omits illustration of dv/dθ before θ_(1S) where thepump chamber 38 starts communicating with the discharge port 222 (therear vane 32 passes through the terminating end portion 221 b of theintake port 221) on the first confinement region A side for each of thepump chambers 38. Further, FIG. 7(b) omits illustration of dv/dθ afterθ_(2E) where the pump chamber 38 is disconnected from the discharge port222 (the front vane 32 passes through the start end portion 221 a of theintake port 221) on the second confinement region B side. FIG. 7(a) is acharacteristic diagram illustrating a relationship between dV/dθ(=Σdv/dθ), which is a sum of dv/dθ of all of the pump chambers 38 incommunication with the discharge port 222, and θ in the ⅓ eccentricitystate. The change amount dV/dθ corresponds to a discharge flow amount Qof the entire pump 1. The change amounts dv/dθ of the individual pumpchambers 38 in communication with the discharge port 222 each contributeto the amount Q. When dv/dθ of some pump chamber 38 in communicationwith the discharge port 222 is a negative value, this pump chamber 38 isin a compression process, and this pump chamber 38 is supplying theliquid to the discharge port 222 (operates in a discharge phase). Thechange amount dv/dθ of this pump chamber 38 contributes to an increasein the amount Q. On the other hand, when dv/dθ of some pump chamber 38in communication with the discharge port 222 is a positive value, thispump chamber 38 is in an expansion process, and this pump chamber 38 isintroducing the liquid from the discharge port 222 (operates in anintake phase). The change amount dv/dθ of this pump chamber 38contributes to a reduction in the amount Q. When the volume changeamount dV/dθ of all of the pump chambers 38 in communication with thedischarge port 222 is a negative value, the pump 1 is discharging thehydraulic liquid by the amount Q that is large if an absolute value ofthis dV/dθ is large.

A high pressure in the pump chamber 38 in communication with thedischarge port 222 is applied to the inner peripheral surface 330 of thecam ring 33, and generates the force for radially moving the cam ring33. A difference in the above-described force between these confinementregions A and B acts on the cam ring 33 in a direction connecting theseregions A and B, and this serves as a cause of oscillation of the camring 33. Now, the number of vanes 32 is the odd number. Therefore, thecommunication between the pump chamber 38 and the discharge port 222 onthe region A side, and the communication between the pump chamber 38 andthe intake port 221 on the region B side are started at differenttimings from each other. More specifically, while some vane 32 ispassing through the region A after being separated from the terminatingend portion 221 b (θ_(1S)) of the intake port 221 (when the pump chamber38 defined in front of this vane 32 is in communication with thedischarge port 222), before this vane 32 reaches the start end portion222 a (θ_(1E)) of the discharge port 222 (the pump chamber 38 definedbehind this vane 32 is separated from the intake port 221 and startscommunicating with the discharge port 222), another vane 32 passingthrough the region B reaches the start end portion 221 a (θ_(2E)) of theintake port 221 (the pump chamber 38 defined behind this vane 32 isseparated from the discharge port 222 and starts communicating with theintake port 221). In other words, when the pump chamber 38 startscommunicating with the intake port 221 on the region B side (thepressure applied from the pump chamber 38 to the inner peripheralsurface 330 of the cam ring 33 is switched from the high pressure to thelow pressure), the pump chamber 38 remains in communication with thedischarge port 222 or the intake port 221 on the region A side (thepressure applied from the pump chamber 38 to the inner peripheralsurface 330 is not largely switched). Further, when the pump chamber 38starts communicating with the discharge port 222 on the region A side(the pressure in the pump chamber 38 that is applied to the innerperipheral surface 330 is switched from the low pressure to the highpressure), the pump chamber 38 remains in communication with thedischarge port 222 or the intake port 221 on the region B side (thepressure applied from the pump chamber 38 to the inner peripheralsurface 330 is not largely switched). Therefore, the difference in theabove-described force that acts in the direction connecting theseregions A and B can be eliminated or reduced compared to when theabove-described timings overlap each other, such as when the pumpchamber 38 starts communicating with the discharge port 222 on theregion A side (the pressure in the pump chamber 38 that is applied tothe inner peripheral surface 330 is switched from the low pressure tothe high pressure) at an approximately same timing as the timing atwhich the pump chamber 38 starts communicating with the intake port 221on the region B side (the pressure in the pump chamber 38 that isapplied to the inner peripheral surface 330 is switched from the highpressure to the low pressure). Therefore, the oscillation of the camring 33 is prevented or reduced, which makes it easy to alleviate thechange in the discharge flow amount Q, thereby reducing the pulsepressure. The number of vanes 32 is not limited to eleven, and may be,for example, nine, thirteen, or the like. In the present embodiment, thedischarge port 222 includes the notch portion 225 on the start endportion 222 a thereof. Therefore, when the pump chamber 38 startscommunicating with the discharge port 222 on the region A side, theinflow of the hydraulic liquid from the discharge port 222 into the pumpchamber 38 is restricted by the notch portion 225, which prevents orcuts down a sudden increase in the pressure in the above-described pumpchamber 38. As a result, the pulse pressure can also be reduced. Theshape of the notch portion 225 is not limited to the shape in thepresent embodiment.

The inner peripheral surface 330 of the cam ring 33 is formed in such amanner that the front vane 32 in the region B passes through the startend portion 221 a (θ_(2E)) of the intake port 221 when the rear vane 32passing through the region A is positioned slightly offset toward theone side located in the direction of the rotation (one side where thestart end portion 222 a (θ_(1E)) of the discharge port 222 is located)from the position ½ pitch away from the terminating end portion 221 b(θ_(1S)) of the intake port 221 (toward the one side located in thedirection of the rotation). In other words, when the front vane 32passing through the region B is positioned slightly offset toward theopposite side located in the direction of the reverse rotation (one sidewhere the terminating end portion 222 b (θ_(2S)) of the discharge port222 is located) from the position ½ pitch away from the terminating endportion 222 b (θ_(2S)) of the discharge port 222 (toward the one sidelocated in the direction of the rotation), the front vane 32 in theregion A passes through the start end portion 222 a (θ_(1E)) of thedischarge port 222. Therefore, at the point that a range occupied by thepump chambers 38 (applying the high pressure to the inner peripheralsurface 330) in communication with the discharge port 222 on the regionB is relatively small, the pump chamber 38 starts communicating with thedischarge port 222 on the region A side and the high pressure is appliedfrom this pump chamber 38 to the inner peripheral surface 330. As aresult, the difference in the above-descried force that acts in thedirection connecting these regions A and B as a whole works in adirection pushing the cam ring 33 toward one side where the eccentricityamount δ thereof increases, which can prevent or cut down anunintentional reduction in δ (a cam drop).

Further, when the pump chamber 38 passing through either the region A orB starts communicating with the discharge port 222 or stopscommunicating with the discharge port 222 with the volume v thereofchanging (increasing or reducing), the volume change amount dV/dθ (thenegative value) of all of the pump chambers 38 in communication with thedischarge port 222 may discontinuously change and the discharge flowamount Q may change every time. The changing direction (increase ordecrease) of this amount Q varies according to whether the volume v ofthis pump chamber 38 is increasing or reducing (the sign of dv/dθ) atthe time of the communication (the disconnection) with the dischargeport 222. More specifically, when the pump chamber 38 passing throughthe region A starts communicating with the discharge port 222, if thevolume v of this pump chamber 38 is in a reducing state (dv/dθ isnegative), the liquid amount (corresponding to the absolute value ofdV/dθ) supplied from all of the pump chambers 38 in communication withthe discharge port 222 to the discharge port 222 suddenly increases dueto the start of the above-described communication. Therefore, the amountQ discontinuously increases. On the other hand, if the volume v of theabove-described pump chamber 38 is in an increasing state (dv/dθ ispositive), the liquid amount supplied from all of the pump chambers 38in communication with the discharge port 222 to the discharge port 222suddenly reduces due to the start of the above-described communication.Therefore, the amount Q discontinuously reduces. Similarly, when thepump chamber 38 passing through the region B is disconnected from thedischarge port 222, the liquid amount supplied from all of the pumpchamber 38 in communication with the discharge port 222 to the dischargeport 222 suddenly increases due to the above-described disconnection(the isolation from the discharge port 222) if the volume v of this pumpchamber 38 is in the increasing state (dv/dθ is positive). Therefore,the amount Q discontinuously increases. On the other hand, the liquidamount supplied from all of the pump chamber 38 in communication withthe discharge port 222 to the discharge port 222 suddenly reduces due tothe above-described disconnection (the isolation from the discharge port222) if the volume v of the above-described pump chamber 38 is in thereducing state (dv/dθ is negative). Therefore, the amount Qdiscontinuously reduces. As described above, the number of vanes 32 isthe odd number, whereby the timing of the communication/disconnectionbetween the discharge port 222 and the pump chamber 38 is asynchronousbetween the region A and the region B. The number of times that theamount Q discontinuously changes while the driving shaft 30 rotates onceis twice when the above-described timing is synchronous between theseregions A and B, and twice (twenty-two times) the number of pumpchambers 38 (the vanes 32) (eleven).

As illustrated in FIG. 3, the sign of dr/dθ in the region A is negativein the maximum eccentricity state. This means that the vane projectionamount r reduces according to the rotation of the roto 31 in the regionA. In other words, the sign of dv/dθ is negative and the volume v of thepump chamber 38 in communication with the discharge port 222 reducesaccording to the rotation of the rotor 31 on the region A side in themaximum eccentricity state. In other words, the above-described pumpchamber 38 in the region A is brought into a compressed process, i.e.,the discharge phase. As a result, a further larger discharge flow amountQ can be secured. Especially, in the case where the variabledisplacement vane pump is used for the power steering apparatus, a largeflow amount is required in the maximum eccentricity state. Securing thelarge flow amount Q as described above can prevent or reducedeterioration of a steering feeling caused due to insufficiency of theflow amount. The sign of dr/dθ is negative in the entire range of theregion A, whereby the above-described effect can be enhanced. Further,if the vane 32 is spaced apart from the inner peripheral surface 330 ofthe cam ring 33 in the region A or B, the pressure pulsation (the pulsepressure) may occur due to a sudden inflow of the liquid from the pumpchamber 38 on the high-pressure side to the pump chamber 38 on thelow-pressure side that sandwich this vane 32. Especially in the maximumeccentricity state, the vane 32 being spaced apart (vane separation)from the inner peripheral surface 330 likely occurs due to, for example,a small number of rotations of the pump. To avoid this risk, the amountr reduces in the direction of the rotation (as the vane 32 travels fromthe terminating end portion 221 b (θ_(1S)) of the intake port 221 towardthe start end portion 222 a (θ_(1E)) of the discharge port 222) in theregion A in the maximum eccentricity state. Therefore, the vaneseparation and thus the occurrence of the pulse pressure can beprevented or reduced. Similarly, as illustrated in FIG. 5, in themaximum eccentricity state, the sign of dr/dθ in the region B isnegative and the volume v of the pump chamber 38 in communication withthe discharge port 222 reduces according to the rotation of the rotor31. In other words, the above-described pump chamber 38 in the region Bis brought into the discharge phase. As a result, a large flow amount Qcan be secured similarly to the above-described region A. Because thesign of dr/dθ is negative in the entire range of the region B, theabove-described effect can be enhanced. Further, the vane separation andthus the occurrence of the pulse pressure can be prevented or reduced inthe region B.

As illustrated in FIG. 4, the sign of dr/dθ is negative in the region Ain the ⅓ eccentricity state. This means that the vane projection amountr reduces according to the rotation of the rotor 31 in the region A. Inother words, the sign of dv/dθ is negative and the volume v of the pumpchamber 38 in communication with the discharge port 222 reducesaccording to the rotation of the rotor 31 on the region A side in the ⅓eccentricity state. Therefore, the above-described pump chamber 38 inthe region A is brought into the discharge phase similarly to themaximum eccentricity state. As a result, a further large flow amount Qcan be secured. Since the sign of dr/dθ is negative in the entire rangeof the region A, the above-described effect can be enhanced. Further,the vane separation can be prevented or reduced in the region A.

As described above, dV/dθ may discontinuously change and the dischargeflow amount Q may discontinuously change (vary) every time the pumpchamber 38 passing through either the confinement region A or B, whilethe volume v thereof is changing, communicates with or is disconnectedfrom the discharge port 222. This may lead to the pulse pressure (thepulsation). As illustrated in FIGS. 4 and 7(b), in the ⅓ eccentricitystate, immediately before O_(1S) where the pump chamber 38 startscommunicating with the discharge port 222 (the rear vane 32 passesthrough the terminating end portion 221 b of the intake port 221) on theregion A side, dv/dθ of this pump chamber 38 (dr/dθ at the rear vane 32)is a negative value (v and r are reducing). Therefore, when this pumpchamber 38 communicates with the discharge port 222 at θ_(1S), theabsolute value of dV/dθ (the negative value) immediately increases, andthis contributes in a direction for increasing the amount Q. On theother hand, immediately before θ_(2E) where the pump chamber 38 isdisconnected from the discharge port 222 (the front vane 32 passesthrough the start end portion 221 a of the intake port 221) on theregion B side, dv/dθ of this pump chamber 38 (in communication with thedischarge port 222) (dr/dθ at the front vane 32) is a positive value (vand r are increasing). Therefore, when this pump chamber 38 isdisconnected from the discharge port 222 at θ_(2E), the absolute valueof dV/dθ (the negative value) suddenly increases, and this alsocontributes in the direction for increasing the amount Q. Theconventional technique has failed to take into consideration such achange in the amount Q when the pump chamber 38 is disconnected from thedischarge port 222 on the region B side, and has left room to reduce thepulse pressure due to that. Especially, the pulse pressure has a furthersignificant influence in the ⅓ eccentricity state. More specifically,noise (whine noise) likely becomes a problem.

The absolute value of dr/dθ gradually reduces, and then graduallyincreases after reaching the extremely small value dr/dθ₁* at θ₁*, asthe vane 32 travels from θ_(1S) toward θ_(1E) in the region A in the ⅓eccentricity state. The absolute value of dv/dθ gradually reduces, andthen gradually increases after reaching the extremely small valuedv/dθ₁* at θ₁** (≈θ₁*), according to the rotation of the rotor 31.Therefore, when the front vane 32 of the pump chamber 38 (the vane 32passing through the region B) reaches the start end portion 221 a of theintake port 221 (the rear vane 32 reaches the terminating end portion222 b of the discharge port 222) and the communication between this pumpchamber 38 and the discharge port 222 is blocked at θ_(2E) on the regionB side, the absolute value of dr/dθ at the position of the rear vane 32of the pump chamber 38 (the vane 32 passing through the region A) fallswithin a predetermined range where the extremely small value dr/dθ₁* isset as a minimum value therein and the absolute value of dv/dθ of thispump chamber 38 falls within a predetermined range where the extremelysmall value dv/dθ₁* is set as a minimum value therein on the region Aside. The absolute value of dv/dθ (the negative value) falling withinthe predetermined range where the extremely value dr/dθ₁* is set as theminimum value therein in the region A means that the rate of thecontraction of the pump chamber 38 contracting in the region A is low,and the rate of the reduction in dV/dθ due to the contraction of thispump chamber 38 is small, i.e., the rate of the increase in the absolutevalue of dV/dθ (the negative value) is small. The sudden increase in theabsolute value of dV/dθ (the negative value) (at θ_(2E)) when the pumpchamber 38 is disconnected from the discharge port 222 on the region Bside is alleviated due to the low rate of the increase in the absolutevalue of dV/dθ (the negative value) on the region A side. In otherwords, when the expanding pump chamber 38 is disconnected from thedischarge port 222 (θ_(2E)) in the region B, the rate of the contractionof the pump chamber 38 communicating with the discharge port 222 andalso contracting is close to dv/dθ₁* and has a small absolute value inthe region A, which prevents or cuts down a considerable change (asudden increase) in dV/dθ. As a result, the change in the amount Q isalleviated, so that the pulse pressure in the entire pump 1 can bereduced. In this manner, the inner peripheral surface 330 of the camring 33 is formed in such a manner that dr/dθ or dv/dθ has theabove-described characteristic in the ⅓ eccentricity state in which thepulse pressure has a significant influence, whereby a function ofreducing the pulse pressure when the pump 1 is driven can be furthereffectively acquired. The above-described advantageous effects can beacquired by forming the inner peripheral surface 330 in such a mannerthat the absolute value of dr/dθ gradually reduces, and then graduallyincreases after reaching the extremely small value, as the vane 32travels from θ_(1S) toward θ_(1E) in at least a part of the region A.

More specifically, the point θ₁* where the absolute value of dr/dθ(dv/dθ) reaches the extremely small value dr/dθ₁* (dv/dθ₁*) is locatedin the range from ⅓ pitch to ⅔ pitch from the terminating end portion221 b (θ_(1S)) of the intake port 221, inclusive, in the region A in the⅓ eccentricity state. Since the number of vanes 32 is the odd number,the front vane 32 passing through the region B passes through the startend portion 221 a (θ_(2E)) of the intake port 221 when the rear vane 32passing through the region A is located at or around the pointθ_(1(1/2)) ½ pitch away from the terminating end portion 221 b (θ_(1S))of the intake port 221. Therefore, θ₁* can be arranged closer to θ_(2E)where dV/dθ suddenly changes on the region B side, by placing θ₁* in theabove-described range (θ_(1(1/3)) to θ_(1(2/3))). This results in thatthe absolute value of dr/dθ (dv/dθ) of the rear vane 32 in the region Asubstantially has the extremely small value dr/dθ₁* (dv/dθ₁*) when thefront vane 32 passes through θ_(2E) in the region B, thereby succeedingin further effectively reducing the pulse pressure.

Further, as illustrated in FIG. 4, the change gradient Δ2 is greaterthan the change gradient Δ1 in the region A in the ⅓ eccentricity state.The change gradient Δ2 greater than Δ1 means that, according to therotation of the rotor 31, compared to how much the rate of thecontraction (the absolute value of dv/dθ) of the pump chamber 38contracting on the region A side reduces on the first half side fromθ₁*, how much the above-described contraction rate increases on thesecond half side from θ₁* after that is larger, i.e., the rate of theincrease in the absolute value of dV/dθ (the negative value) is high onthe above-described second half side. The volume v of the pump chamber38 in communication with the discharge port 22 on the region A sidefurther swiftly reduces on the above-described second half side and theabsolute value of dV/dθ (the negative value) increases at the high rateon the above-described second half side, which allieviates the change indV/dθ (after θ_(2E)) after the pump chamber 38 is disconnected from thedischarge port 222 and the absolute value of dV/dθ (the negative value)suddenly increases on the region B side (an angle δ illustrated in FIG.7(a) increases). Therefore, the pulse pressure can be furthereffectively reduced. It is preferable that Δ2/Δ1 is 1.1 or higher. Inthis case, the change in dV/dθ after the pump chamber 38 is disconnectedfrom the discharge port 222 (after θ_(2E)) on the region B side can befurther effectively reduced. It is preferable that Δ2/Δ1 is 1.15 orhigher. By that, the above-described change in dV/dθ can be furthereffectively reduced. In the present embodiment, Δ2/Δ1 is approximately1.24 (i.e., 1.15 or higher), and therefore can acquire theabove-described effect.

The characteristic of dr/dθ or the like in the maximum eccentricitystate may also be set in a similar manner to the ⅓ eccentricity state,besides the above-described setting. For example, the inner peripheralsurface 330 of the cam ring 33 may be formed in such a manner that theabsolute value of dr/dθ gradually reduces, and then gradually increasesafter reaching the extremely small value, as the vane 32 travels fromθ_(1S) toward θ_(1E) in the region A in the maximum eccentricity state.Alternatively, the inner peripheral surface 330 of the cam ring 33 maybe formed in such a manner that the amount r gradually increases in theregion B at least in a partial (the θ_(2E) side) range continuous fromthe terminating end portion (θ_(2E)) thereof. In these cases,advantageous effects similar to those in the above-described ⅓eccentricity state can also be acquired.

In the comparative example indicated by the long dashed double-dottedline in FIG. 6, the inner peripheral surface 330 of the cam ring 33 isformed in such a manner that the change rate of dr/dθ with respect to θis a positive value in the entire range of the region B in the minimumeccentricity state. Therefore, the absolute value of the above-describedchange rate of dr/dθ generally does not change as the vane 32 travelsfrom θ_(2S) toward θ_(2E) in the region B in the ⅓ eccentricity state.As a result, dr/dθ has a large change gradient in the range from θ_(2S)to θ_(2E) and dr/dθ has a great magnitude at θ_(2E) (when thecommunication between the pump chamber 38 and the discharge port 222 isblocked in the region B) in the ⅓ eccentricity state. On the other hand,in the present embodiment, the inner peripheral surface 330 is formed insuch a manner that there is the region Ba where the above-describedchange rate of dr/dθ has at least a negative value (there are the θregion Ba where the above-describe change rate of dr/dθ has a negativevalue and the θ region Bb where the above-described change rate of dr/dθhas a positive value) in the region B in the minimum eccentricity stateas indicated by a solid line in FIG. 6. Therefore, the absolute value ofthe above-described change rate of dr/dθ (the slope of the graph ofdr/dθ with respect to θ) generally gradually reduces as the vane 32travels from θ_(2S) toward θ_(2E) in the region B in the ⅓ eccentricitystate. As a result, dr/dθ has a small change gradient in the range fromθ_(2S) to θ_(2E) in the ⅓ eccentricity state. Therefore, dr/dθ_(2E),which is dr/dθ at θ_(2E), has a small magnitude. In other words, themagnitude dv/dθ_(2E) of dv/dθ at θ_(2E), i.e., a width of the change indV/dθ when the communication between the pump chamber 38 and thedischarge port 222 is blocked in the region B is reduced as illustratedin FIG. 7. Therefore, the change in the amount Q is alleviated, and thepulse pressure is reduced.

The sign of dr/dθ (dv/dθ) may be positive in a partial range (the θ_(1E)side) of the region A. In other words, the amount r (the volume v) maygradually increase in the direction of the rotation of the rotor 31 (asthe vane 32 travels from the θ_(1S) side toward θ_(1E)) in this range.This means that the pressure in the pump chamber 38 may increaseexcessively (for example, increase to higher than the dischargepressure) on the θ_(1E) side in the region A in the minimum eccentricitystate when the inner peripheral surface 330 of the cam ring 33 is formedin such a manner that the amount r gradually reduces in the region A inthe maximum eccentricity state. In this case, a large difference isgenerated in the force applied to the inner peripheral surface 330between the region A and the region B, so that the cam ring 33 mayoscillate (the pulse pressure may occur). To avoid this risk, thedifference in the above-described force and thus the occurrence of thepulse pressure can be prevented or reduced by, for example, forming theinner peripheral surface 330 in such a manner that the sign of dr/dθ(dv/dθ) becomes positive in at least a partial range (the θ_(1E) side)of the region A in the minimum eccentricity state.

Further, the sign of dr/dθ (dv/dθ) may be negative in at least a partialrange (the θ_(2E) side) of the region B. In other words, the amount r(the volume v) may gradually reduce in the direction of the rotation ofthe rotor 31 (as the vane 32 travels from the θ_(2S) side toward θ_(2E))in this rage. In this case, the absolute value of dV/dθ (the negativevalue) suddenly reduces when the pump chamber 38 is disconnected fromthe discharge port 222 at θ_(2E) in the region B. This contributes inthe direction for reducing the amount Q. At this time, if dv/dθ of thepump chamber 38 communicating with the discharge port 222 while passingthrough the region A is a negative value (if v is reducing), thiscontributes in the direction for increasing the amount Q as describedabove. Therefore, the change (the sudden reduction) in the amount Q dueto the sudden change in dV/dθ at θ_(2E) on the region B side can becontrolled or cut down by making an arrangement in such a manner thatdv/dθ (dr/dθ) on the region A side changes so as to cause the absolutevalue of dv/dθ (the negative value) on the region A side to have a largevalue at the time of this sudden change. More specifically, the innerperipheral surface 330 of the cam ring 33 is formed in such a mannerthat the absolute value of dr/dθ (the negative value) graduallyincreases and then gradually reduces after reaching an extremely largevalue in the direction of the rotation of the rotor 31 (as the vane 32travels from θ_(1S) toward θ_(1E)) in the region A. The absolute valueof dv/dθ (the negative value) (the rate of the contraction of the pumpchamber 38) gradually increases and then gradually reduces afterreaching an extremely large value according to the rotation of the rotor31. As a result, the change (the sudden reduction) in the amount Q dueto the sudden change in dV/dθ on the region B side can be alleviated bythe change (the facilitated increase) in the amount Q due to theincrease in the absolute value of dv/dθ (amplification of the negativevalue toward an extremely large value side) on the region A side. Inother words, the rate of the contraction (the absolute value of dv/dθ)of the pump chamber 38 contracting in the region A increases toward theextremely large value when the contracting pump chamber 38 isdisconnected from the discharge port 222 in the region B (θ_(2E)), bywhich a large change in dV/dθ is prevented or cut down.

On the other hand, if dv/dθ of the pump chamber 38 communicating withthe discharge port 222 while passing through the region A is a positivevalue (if v is increasing), this contributes in the direction forreducing the amount Q. Therefore, the change (the sudden reduction) inthe amount Q due to the sudden change in dV/dθ at θ_(2E) on the region Bside can be controlled or cut down by making an arrangement in such amanner that dv/dθ (dr/dθ) on the region A side changes so as to causethe absolute value of dv/dθ (the positive value) on the region A side tohave a small value at the time of this sudden change. More specifically,the inner peripheral surface 330 of the cam ring 33 is formed in such amanner that the absolute value of dr/dθ (the positive value) graduallyreduces and then gradually increases after reaching an extremely smallvalue in the direction of the rotation of the rotor 31 in the region A.The absolute value of dv/dθ (the rate of the expansion of the pumpchamber 38) gradually reduces and then gradually increases afterreaching an extremely small value according to the rotation of the rotor31. As a result, the change (the sudden reduction) in the amount Q dueto the sudden change of dV/dθ on the region B side can be alleviated bythe change (a suppressed reduction) in the amount Q due to the reductionin the absolute value of dv/dθ (suppression of the positive value towardan extremely small value side) on the region A side.

In each of the above-described cases, the characteristic of dr/dθ or thelike may be exchanged between the region A side and the region B side.In other words, the inner peripheral surface 330 may be formed in such amanner that dv/dθ (dr/dθ) on the region B side changes in a directionfor reducing the change in dv/dθ (dr/dθ) when the pump chamber 38 startscommunicating with the discharge port 222 according to the rotation ofthe rotor 31 on the region A side (θ_(1S)). In this case, the change inthe amount Q due to the sudden change in dV/dθ on the region A side canbe reduced. An important point is that the present embodiment can berealized as long as, at the timing when the pump chamber 38 communicateswith or is disconnected from the discharge port 222 on one sidecorresponding to one of the confinement regions or a timing closethereto, the change in dv/dθ (dr/dθ) on another side corresponding tothe other of the confinement regions has an extreme value in thedirection for reducing the change in dv/dθ (dr/dθ) at the time of theabove-described communication/disconnection.

The range of each of the regions A and B does not have to beapproximately one pitch, and may be, for example, 1.5 pitch or the like.Setting the size of the region to approximately one pitch or larger canprevent the pump chamber 38 passing through either the region A or Bfrom communicating with both the intake port 221 and the discharge port222. Reducing the range to as small as approximately one pitch allowsthe pump 1 to further efficiently intake and discharge the hydraulicliquid as a whole, thereby increasing the discharge flow amount.

In the pump housing 2, the pair of surfaces (the surface 210 of thefront body 21 on the z-axis negative direction side and the surface 220of the side plate 22 on the z-axis positive direction side) facing theregion A and the region B in the direction along the rotational axis ofthe driving shaft 30 (the z-axis direction) is formed so as to extend inparallel with each other and is each shaped into a flat surface.Therefore, the volume v of the pump chamber 38 does not change in thez-axis direction, and the volume v of the pump chamber 38 in each of theregions A and B does not change depending on the shape of the surface ofthe pump housing 2. In other words, the change in the shape of the innerperipheral surface 330 of the cam ring 33 in the direction of therotation of the rotor 31 (dr/dθ, hereinafter this will be referred to asa cam profile) is generally directly reflected as the change in thevolume v. Therefore, the characteristic of the volume change dv/dθ ofthe pump chamber 38 in each of the regions A and B can be adjusted onlyby an adjustment of the change in the above-described shape (the camprofile). Therefore, the adjustment for reducing the pulse pressure canbe easily achieved. The cam profile in each of the eccentricity statesmay be adjusted not only by the adjustment of the shape of the innerperipheral surface 330 of the cam ring 33 itself but also by anadjustment of the shape of the inner peripheral surface 340 (the secondsupport surface 342) of the adaptor ring 34 (changing the position ofthe central axis P in the y-axis direction relative to the shaft centerO according to the eccentricity amount δ).

The discharge port 222 includes the notch portion 225 only on the startend portion 222 a side thereof (the terminating end portion θ_(IE) sideof the region A). In other words, there is no notch portion on theterminating end portion 222 b side of the discharge port 222 (the startend portion θ_(2S) side of the region B). Actually, it is alsoconceivable to, for example, by providing a notch portion like the onein communication with the intake port 221 via the pump chamber 38 on theterminating end portion 222 b side of the discharge port 222, reduce thepulse pressure due to the change in the volume when the communication ofthis pump chamber 38 with the discharge port 222 is blocked. However, inthis case, the discharge port 222 and the intake port 221 are incommunication with each other via the notch portion (via the pumpchamber 38 in communication with the notch portion) in the region B, sothat a leak amount increases. Therefore, this method may lead todeterioration of the pump efficiency. Then, it is also conceivable toemploy a layout that prevents the discharge port 222 and the intake port221 from communicating with each other via the notch portion (via thepump chamber 38 in communication with the notch portion) while providingthe notch portion on the terminating end portion 222 b side of thedischarge port 222. However, this case results in that, with the rearvane 32 overlapping with the notch portion (with the notch portioncausing a change in the volume of the pump chamber 38 sandwiched by thefront vane 32 and the rear vane 32) in the region B, the projectionamount r of the front vane 32 (the volume v of this pump chamber 38) isadjusted by the cam profile. Therefore, it may become difficult toappropriately reduce the above-described pulse pressure due to thechange in the volume at the time of the disconnection between this pumpchamber 38 and the discharge port 222, by adjusting the shape of theinner peripheral surface 330 of the cam ring 33. On the other hand, inthe present embodiment, no notch portion is provided on the terminatingend portion 222 b side of the discharge port 222. Therefore, the presentembodiment can further effectively achieve both the reduction in thepulse pressure and the prevention or reduction in the deterioration ofthe pump efficiency. In the region A, the notch portion 225 on the startend portion 222 a side of the discharge port 222 is not in communicationwith the intake port 221 via the pump chamber 38. Therefore, thedeterioration of the pump efficiency can be prevented or reduced.Further, this method results in that, without the front vane 32overlapping with the notch portion 225 (with the notch portion 225causing no change in the volume of the pump chamber 38 sandwichedbetween the front vane 32 and the rear vane 32), the projection amount rof the front vane 32 (the volume v of this pump chamber 38) is adjustedby the cam profile. Therefore, the above-described pulse pressure due tothe change in the volume when this pump chamber 38 starts communicatingwith the discharge port 222 (the notch portion 225) can be easilyappropriately reduced by the adjustment of the above-described campprofile.

Second Embodiment

The inner peripheral surface 330 of the cam ring 33 is formed in thefollowing manner. In the maximum eccentricity state, as illustrated inFIG. 8, the sign of the change rate dr/dθ is negative in the entirerange of the first confinement region A, and the sign of dr/dθ isnegative at least on one side where the start end portion 221 a (θ_(2E))of the intake port 221 is located in the second confinement region B. Inthe ⅓ eccentricity state, as illustrated in FIG. 9, the sign of dr/dθ isnegative in the region A. The absolute value of dr/dθ gradually reduces,and then gradually increases after reaching the extremely small valuedr/dθ₁* at θ₁*, as the vane 32 travels from the terminating end portion221 b (θ_(1S)) of the intake port 221 toward the start end portion 222 a(θ_(1E)) of the discharge port 222. The point θ₁* is located in a rangefrom ½ pitch to ⅔ pitch from θ_(1S) inclusive. In other words, the pointθ₁* is located between the point θ_(1(1/2)) positioned ½ pitch away fromθ_(1S), and the point θ_(1(2/3)) positioned ⅔ pitch away from θ_(1S).The region A is one pitch. Therefore, θ₁* is located on a second halfside (a θ_(1(2/3)) side) of the range of the central portion (θ_(1(1/3))to θ_(1(2/3))) when the region A is divided into the three portions. Inthe ⅓ eccentricity state, the second change gradient Δ2 is greater thanthe first change gradient Δ1 (Δ1<Δ2). In the present embodiment, Δ2/Δ1is approximately 1.76. Other configurations are similar to the firstembodiment.

Similarly to the first embodiment, when the rear vane 32 passing throughthe region A is located slightly offset toward the θ_(1E) side from theposition ½ pitch away from θ_(1S), the front vane 32 in the region Bpasses through the start end portion 221 a of the intake port 221. Inthe present embodiment, in the ⅓ eccentricity state, θ₁* is located inthe range from the position ½ pitch away from θ_(1S) to the position ⅔pitch away from θ_(1S) in the region A. As a result, the point θ₁* wherethe absolute value of the contraction rate dv/dθ (the negative value) ofthe pump chamber 38 communicating with the discharge port 222 (whilealso contracting) on the region A side reduces to dv/dθ₁* can be furtheradapted to (arranged closer to) the point θ_(2E) where the (expanding)pump chamber 38 is disconnected from the discharge port 222 on theregion B side. Therefore, the pulse pressure can be further effectivelyreduced. Further, since Δ2/Δ1 is approximately 1.76 (i.e., 1.15 orhigher), the change in dV/dθ after the pump chamber 38 is disconnectedfrom the discharge port 222 on the region B side (after θ_(2E)) can befurther effectively controlled or reduced. Other advantageous effects ofthe second embodiment are similar to the first embodiment.

Other Embodiments

Having described the vane pump according to the present invention basedon the embodiments thereof, the specific configuration of the presentinvention is not limited to the embodiments, and the present inventionalso includes a design modification and the like thereof made within arange that does not depart from the spirit of the present invention. Forexample, the vane pump to which the present invention is applied may beused as a hydraulic supply source of another apparatus (an engine of avehicle or the like) than the power steering apparatus. The slots (orthe vanes) of the vane pump do not have to extend in the radialdirection of the rotor, and may be inclined at some angle from theradial direction of the rotor. The specific configuration of the camring control mechanism is not limited to the configuration in the firstembodiment, and may be, for example, such a configuration that thepressure is also supplied to the first chamber and the first chamberfunctions as the fluid pressure chamber.

[Technical Ideas Recognizable from Embodiments]

Technical ideas (or technical solutions, the same applies hereinafter)recognizable from the above-described embodiments can be provided asdescribed below.

-   (1) One aspect of a variable displacement vane pump according to the    present technical ideas, in one embodiment thereof, includes

a pump housing including a pump element containing portion,

a driving shaft supported on the pump housing,

a rotor provided in the pump housing and configured to be rotationallydriven by the driving shaft while also including an odd number of slotsin a circumferential direction,

an odd number of vanes provided in the slots in a manner projectabletherefrom and retractable therein,

a cam ring movably provided in the pump element containing portion andannularly formed while forming a plurality of pump chambers on an innerperipheral side in cooperation with the rotor and the vanes,

an intake port formed in the pump housing and opened to a region where avolume of each of the plurality of pump chambers increases according toa rotation of the rotor,

a discharge port formed in the pump housing and opened to a region wherethe volume of each of the plurality of pump chambers reduces accordingto the rotation of the rotor, and

a cam ring control mechanism provided in the pump housing and configuredto control an amount of eccentricity of the cam ring from the rotor.

Then, assume that a distance between the vanes adjacent to each other ina direction around a rotational axis of the driving shaft is one pitch,a vane projection amount refers to a distance from a center of arotation of the driving shaft to an inner peripheral surface of the camring, and

a first confinement region is defined to be a region between aterminating end portion of the intake port and a start end portion ofthe discharge port.

The inner peripheral surface of the cam ring is formed in the followingmanner. At least in a part of the first confinement region, an absolutevalue of a change rate of the vane projection amount with respect to arotational amount of the rotor gradually reduces and then graduallyincreases after reaching an extremely small value as the vane travelsfrom the terminating end portion of the intake port toward the start endportion of the discharge port.

A point where the absolute value of the change rate reaches theextremely small value is located in a range from ⅓ pitch to ⅔ pitch fromthe end portion of the intake port, inclusive.

In the first confinement region, a change gradient of the change ratesince the absolute value of the change rate reaches the extremely smallvalue until stopping the increase is greater than a change gradient ofthe change rate since the absolute value of the change rate starts thereduction until reaching the extremely small value.

-   (2) In a further preferable embodiment, the variable displacement    vane pump according to the above-described embodiment is configured    in the following manner. Assuming that a second confinement region    is defined to be a region between an end portion of the discharge    port and a start end portion of the intake port, in the pump    housing, a pair of surfaces facing the first confinement region in a    direction along the rotational axis of the driving shaft is formed    so as to extend in parallel with each other and each shaped as a    flat surface, and a pair of surfaces facing the second confinement    region in the direction along the rotational axis of is formed so as    to extend in parallel with each other and each shaped as a flat    surface.-   (3) In another preferable embodiment, the variable displacement vane    pump according to any of the above-described embodiments is    configured in the following manner. The inner peripheral surface of    the cam ring is formed in such a manner that the point where the    absolute value of the change rate reaches the extremely small value    is located in a range from ½ to ⅔ pitch from the end portion of the    intake port, inclusive, at least in a part of the first confinement    region.-   (4) In still another preferable embodiment, the variable    displacement vane pump according to any of the above-described    embodiments is configured in the following manner. The inner    peripheral surface of the cam ring is formed in such a manner that,    when the cam ring is moved by ⅓ of an entire eccentricity amount    from a position where the eccentricity amount of the cam ring is    maximized toward a position where the eccentricity amount of the cam    ring is minimized, the absolute value of the change rate gradually    reduces and then gradually increases after reaching the extremely    small value as the vane travels from the end portion of the intake    port toward the start end portion of the discharge port at least in    a partial range of the first confinement region, the point where the    absolute value of the change rate reaches the extremely small value    is located in a range from ⅓ pitch to ⅔ pitch from the end portion    of the intake port, inclusive, and the change gradient of the change    rate since the absolute value of the change rate reaches the    extremely small value until stopping the increase is greater than    the change gradient of the change rate since the absolute value of    the change rate starts the reduction until reaching the extremely    small value in the first confinement region.-   (5) In still another preferable embodiment, the variable    displacement vane pump according to any of the above-described    embodiments is configured in the following manner. The inner    peripheral surface of the cam ring is formed in such a manner that    the vane projection amount constantly reduces as the vane travels    from the end portion of the intake port toward the start end portion    of the discharge port according to the rotation of the rotor in the    first confinement region when the cam ring is located at the    position where the eccentricity amount of the cam ring is maximized.-   (6) In still another preferable embodiment, the variable    displacement vane pump according to any of the above-described    embodiments is configured in the following manner. The inner    peripheral surface of the cam ring is formed in such a manner that a    ratio of the change gradient of the change rate since the absolute    value of the change rate reaches the extremely small value until    stopping the increase to the change gradient of the change rate    since the absolute value of the change rate starts the reduction    until reaching the extremely small value is 1.1 or higher in the    first confinement region.-   (7) In still another preferable embodiment, the variable    displacement vane pump according to any of the above-described    embodiments is configured in the following manner. The inner    peripheral surface of the cam ring is formed in such a manner that a    ratio of the change gradient of the change rate since the absolute    value of the change rate reaches the extremely small value until    stopping the increase to the change gradient of the change rate    since the absolute value of the change rate starts the reduction    until reaching the extremely small value is 1.15 or higher in the    first confinement region.-   (8) In still another preferable embodiment, the variable    displacement vane pump according to any of the above-described    embodiments is configured in the following manner. The inner    peripheral surface of the cam ring is formed in such a manner that    there is a region where a change rate of the change rate with    respect to the rotational amount of the rotor has a negative value    in the second confinement region, which is the region from the end    portion of the discharge port to the start end portion of the intake    port, when the cam ring is located at the position where the    eccentricity amount of the cam ring is minimized.-   (9) In still another preferable embodiment, the variable    displacement vane pump according to any of the above-described    embodiments is configured in the following manner. The discharge    port includes a notch portion only on a start end portion side of    the discharge port.-   (10) Another aspect of a variable displacement vane pump according    to the present technical ideas, in one embodiment thereof, includes

a pump housing including a pump element containing portion,

a driving shaft supported on the pump housing,

a rotor provided in the pump housing and configured to be rotationallydriven by the driving shaft while also including an odd number of slotsin a circumferential direction, an odd number of vanes provided in theslots in a manner projectable therefrom and retractable therein,

a cam ring movably provided in the pump element containing portion andannularly formed while forming a plurality of pump chambers on an innerperipheral side in cooperation with the rotor and the vanes,

an intake port formed in the pump housing and opened to a region where avolume of each of the plurality of pump chambers increases according toa rotation of the rotor,

a discharge port formed in the pump housing and opened to a region wherethe volume of each of the plurality of pump chambers reduces accordingto the rotation of the rotor, and

a cam ring control mechanism provided in the pump housing and configuredto control an amount of eccentricity of the cam ring from the rotor.

Then, assume that a distance between the vanes adjacent to each other ina direction around a rotational axis of the driving shaft is one pitch,a vane projection amount refers to a distance from a center of arotation of the driving shaft to an inner peripheral surface of the camring, and a first confinement region is defined to be a region from aterminating end portion of the intake port to a start end portion of thedischarge port.

The inner peripheral surface of the cam ring is formed in such a mannerthat, when the cam ring is moved by ⅓ of an entire eccentricity amountfrom a position where the eccentricity amount of the cam ring ismaximized toward a position where the eccentricity amount of the camring is minimized, an absolute value of a change rate of the vaneprojection amount with respect to a rotational amount of the rotorgradually reduces and then gradually increases after reaching anextremely small value as the vane travels from the terminating endportion of the intake port toward the start end portion of the dischargeport at least in a part of the first confinement region,

a point where the absolute value of the change rate reaches theextremely small value is located in a range from ⅓ pitch to ⅔ pitch fromthe terminating end portion of the intake port, inclusive, and

a change gradient of the change rate since the absolute value of thechange rate reaches the extremely small value until stopping theincrease is greater than a change gradient of the change rate since theabsolute value of the change rate starts the reduction until reachingthe extremely small value in the first confinement region.

-   (11) In a further preferable embodiment, the variable displacement    vane pump according to the above-described embodiment is configured    in the following manner. The inner peripheral surface of the cam    ring is formed in such a manner that the vane projection amount    constantly reduces as the vane travels from the terminating end    portion of the intake port toward the start end portion of the    discharge port according to the rotation of the rotor in the first    confinement region when the cam ring is located at the position    where the eccentricity amount of the cam ring is maximized.-   (12) In a further preferable embodiment, the variable displacement    vane pump according to any of the above-described embodiments is    configured in the following manner. The inner peripheral surface of    the cam ring is formed in such a manner that there is a region where    a change rate of the change rate with respect to the rotational    amount of the rotor has a negative value in a second confinement    region, which is a region from a terminating end portion of the    discharge port to a start end portion of the intake port, when the    cam ring is located at the position where the eccentricity amount of    the cam ring is minimized.

Although only some exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teaching andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention. It is alsopossible to combine together the above-described embodiments as desired.

The present application claims priority to Japanese Patent ApplicationNo. 2016-058149 filed on Mar. 23, 2016. The entire disclosure ofJapanese Patent Application No. 2016-058149 filed on Mar. 23, 2016including specification, claims, drawings and summary is incorporatedherein by reference in its entirety.

REFERENCE SIGNS LIST

-   1 vane pump-   2 pump housing-   200 recessed portion (pump element containing portion)-   221 intake port-   222 discharge port-   30 driving shaft-   31 rotor-   311 slot-   32 vane-   33 cam ring-   330 inner peripheral surface-   38 pump chamber-   4 control portion (cam ring control mechanism)-   A first confinement region-   B second confinement region

What is claimed is:
 1. A variable displacement vane pump comprising: apump housing including a pump element containing portion; a drivingshaft supported on the pump housing; a rotor provided in the pumphousing and configured to be rotationally driven by the driving shaft,the rotor also including an odd number of slots in a circumferentialdirection of the rotor; an odd number of vanes provided in the slots ina manner projectable therefrom and retractable therein; a cam ringmovably provided in the pump element containing portion and annularlyformed, the cam ring forming a plurality of pump chambers on an innerperipheral side of the cam ring in cooperation with the rotor and thevanes; an intake port formed in the pump housing and opened to a regionwhere a volume of each of the plurality of pump chambers increasesaccording to a rotation of the rotor; a discharge port formed in thepump housing and opened to a region where the volume of each of theplurality of pump chambers reduces according to the rotation of therotor; and a cam ring control mechanism provided in the pump housing andconfigured to control an amount of eccentricity of the cam ring from therotor, wherein the cam ring has an inner peripheral surface formed insuch a manner that, assuming that a distance between the vanes adjacentto each other in a direction around a rotational axis of the drivingshaft is one pitch, in a first confinement region that is a region froma terminating end portion of the intake port to a start end portion ofthe discharge port, a vane projection amount, which is a distance from acenter of a rotation of the driving shaft to the inner peripheralsurface of the cam ring, gradually increases from the terminating endportion of the intake port and then gradually reduces toward the startend portion of the discharge port after passing through a point wherethe vane projection amount reaches a maximum value, the point where thevane projection amount reaches the maximum value is located in a rangefrom ⅓ pitch to ⅔ pitch from the terminating end portion of the intakeport, inclusive, and an absolute value of a gradient of a cam profile,which is a change rate of the vane projection amount, is larger in arange from a position ½ pitch away from the terminating end portion ofthe intake port to the start end portion of the discharge port than in arange from the terminating end portion of the intake port to ½ pitchtherefrom.
 2. The variable displacement vane pump according to claim 1,wherein, assuming that the second confinement region is a region betweena terminating end portion of the discharge port and a start end portionof the intake port, the pump housing has a pair of surfaces facing thefirst confinement region and the second confinement region in adirection along the rotational axis of the driving shaft, the pair ofsurfaces being formed so as to extend in parallel with each other andeach shaped as a flat surface.
 3. The variable displacement vane pumpaccording to claim 1, wherein the cam ring is formed in such a mannerthat the point where the vane projection amount reaches the maximumvalue is located in a range from a position ½ away from the terminatingend portion of the intake port to a position ⅔ away from the terminatingend portion of the intake port.
 4. The variable displacement vane pumpaccording to claim 1, wherein the inner peripheral surface of the camring is formed in such a manner that, when the cam ring is moved by ⅓ ofan entire eccentricity amount from a position where the eccentricityamount of the cam ring is maximized toward a position side where theeccentricity amount of the cam ring is minimized, in the firstconfinement region that is the region between the terminating endportion of the intake port to the start end portion of the dischargeport, the vane projection amount, which is the distance from the centerof the rotation of the driving shaft to the inner peripheral surface ofthe cam ring, gradually increases from the terminating end portion ofthe intake port and then gradually reduces toward the start end portionof the discharge port after passing through the point where the vaneprojection amount reaches the maximum value, the point where the vaneprojection amount reaches the maximum value is located in a range from ⅓pitch to ⅔ pitch from the terminating end portion of the intake port,inclusive, and the absolute value of the gradient of the cam profile,which is the change rate of the vane projection amount, is larger in therange from the position ½ pitch away from the terminating end portion ofthe intake port to the start end portion of the discharge port than inthe range from the terminating end portion of the intake port to ½ pitchtherefrom.
 5. The variable displacement vane pump according to claim 4,wherein the cam ring is formed in such a manner that the vane projectionamount constantly reduces according to the rotation of the rotor in thefirst confinement region when the cam ring is located at the positionwhere the eccentricity amount of the cam ring is maximized.
 6. Thevariable displacement vane pump according to claim 1, wherein the camring is formed in such a manner that the absolute value of the gradientof the cam profile satisfies 1.1<=(the range from the position ½ pitchaway from the terminating end portion of the intake port to the positionof the start end portion of the discharge port)/(the range from theposition of the terminating end portion of the intake port to theposition ½ pitch therefrom).
 7. The variable displacement vane pumpaccording to claim 6, wherein the cam ring is formed in such a mannerthat the absolute value of the gradient of the cam profile satisfies1.15<=(the range from the position ½ pitch away from the terminating endportion of the intake port to the position of the start end portion ofthe discharge port)/(the range from the position of the terminating endportion of the intake port to the position ½ pitch therefrom).
 8. Thevariable displacement vane pump according to claim 1, wherein the camring is formed so as to have a region where the gradient of the camprofile has a negative value in a second confinement region, which is aregion from a terminating end portion of the discharge port to a startend portion of the intake port, when the cam ring is located at aposition where an eccentricity amount of the cam ring is minimized. 9.The variable displacement vane pump according to claim 1, wherein thedischarge port includes a notch portion only on a start end portion sideof the discharge port.
 10. A variable displacement vane pump comprising:a pump housing including a pump element containing portion; a drivingshaft supported on the pump housing; a rotor provided in the pumphousing and configured to be rotationally driven by the driving shaft,the rotor also including an odd number of slots in a circumferentialdirection of the rotor; an odd number of vanes provided in the slots ina manner projectable therefrom and retractable therein; a cam ringmovably provided in the pump element containing portion and annularlyformed, the cam ring forming a plurality of pump chambers on an innerperipheral side of the cam ring in cooperation with the rotor and thevanes; an intake port formed in the pump housing and opened to a regionwhere a volume of each of the plurality of pump chambers increasesaccording to a rotation of the rotor; a discharge port formed in thepump housing and opened to a region where the volume of each of theplurality of pump chambers reduces according to the rotation of therotor; and a cam ring control mechanism provided in the pump housing andconfigured to control an amount of eccentricity of the cam ring from therotor, wherein the cam ring has an inner peripheral surface formed insuch a manner that, assuming that a distance between the vanes adjacentto each other in a direction around a rotational axis of the drivingshaft is one pitch, when the cam ring is moved by ⅓ of an entireeccentricity amount from a position where the eccentricity amount of thecam ring is maximized toward a position side where the eccentricityamount of the cam ring is minimized, in a first confinement region thatis a region from a terminating end portion of the intake port to a startend portion of the discharge port, a vane projection amount, which is adistance from a center of a rotation of the driving shaft to the innerperipheral surface of the cam ring, gradually increases from theterminating end portion of the intake port and then gradually reducestoward the start end portion of the discharge port after passing througha point where the vane projection amount reaches a maximum value, thepoint where the vane projection amount reaches the maximum value islocated in a range from ⅓ pitch to ⅔ pitch from the terminating endportion of the intake port, inclusive, and an absolute value of agradient of a cam profile, which is a change rate of the vane projectionamount, is larger in a range from a position ½ pitch away from theterminating end portion of the intake port to the start end portion ofthe discharge port than in a range from the terminating end portion ofthe intake port to ½ pitch therefrom.
 11. The variable displacement vanepump according to claim 10, wherein the cam ring is formed in such amanner that the vane projection amount constantly reduces according tothe rotation of the rotor in the first confinement region when the camring is located at the position where the eccentricity amount of the camring is maximized.
 12. The variable displacement vane pump according toclaim 10, wherein the cam ring is formed so as to have a region wherethe gradient of the cam profile has a negative value in a secondconfinement region, which is a region from a terminating end portion ofthe discharge port to a start end portion of the intake port, when thecam ring is located at a position where an eccentricity amount of thecam ring is minimized.